(Chapter 22) Fundamental Concepts of Data Communications (149-166)

BOOK REVIEW IN COMMUNICATIONS

FUNDAMENTAL CONCEPTS OF DATA COMMUNICATIONS

CHAPTER 22 #

Electronic Communications System By Wayne Tomasi

DEFINITIONS

1)

Often used to represent characters and symbols such as letters, digits and punctuation marks. Another terms:  character codes  character sets  symbol codes  character languages

2)

Sometimes called the Telex Code, was the first fixed length character developed for machines rather than forpeople.

3)

A French postal engineer who developed the baudot code in 1875 and named after Emile Baudot, an early pioneer in telegraph printing.

4)

Fixed-length source code.

5)

Stands for United States of America Standard Code for Information Exchange, better known as ASCII-63.

6)

The standard character set for source coding the alphanumeric character set that humans understand but computers do not (computers only understand 1s and 0s). It is a seven bit fixed-length character set.

7)

Fixed-length source code.

8)

Extended binary coded decimal interchange-code, an eight bit fixed length character developed in 1962 by International Business Machines Corporation.

Prepared By : MARY JANE R. ROGELIO

TERMS

Data Communications Codes

Baudot Code

Thomas Murray

Fixed Length Block Code

USASCII

ASCII

Fixed Length Block Code

EBCDIC

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10)

Electronic Communications System By Wayne Tomasi

Omnipresent block and white striped stickers that seem to appear or virtually every consumer item in the US and most of the rest of the world.

It has spaces or gaps between characters. Each character is independent of every other character.

11)

It does not include spaces between characters. An example is Universal Product Code.

12)

It stores data in two dimensions in contrasts with conventional linear bar codes which stores data along only one axis.

Bar Codes

Discrete Code

Continuous Code

2D code

It uses an alphanumeric code similar to ASCII code. It contains 9 vertical elements (5 bars & 4 spaces). It consists of 36 unique codes representing the 10 digits and 26 uppercase letters. 13)

Code-39 Other Names:  Code 3 of 9  3 of 9 code

14)

A continuous code since there are no interchangeable spaces. Each UPC label contains a 12-digit number.

15)

It consists of a 101 (bar-soace-bar) sequence, which is used to frame the 12 digit UPC number.

16)

It separates the left and right halves of the label and consists of two long bars in the center of the label.

Prepared By : MARY JANE R. ROGELIO

Universal Product Code

Start & Stop Guard Pattern

Center Guard Frame

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Electronic Communications System By Wayne Tomasi

Caused by electrical interference from natural sources Classification of Data Com Errors:  single bit  multiple bit  burst

Transmission Errors

Categories of Error Control :  Error Detection  Error Correction

18)

Errors with only one bit within a given a given string is in error.

19)

Errors with two or more non-consecutive bits within a message.

20)

Errors when to or more consecutive bits within a given data string are in error. It can affect one or more characters within a message.

21)

The theoretical (Mathematical) expectation of the rate at which errors will occur.

22)

The actual historical record of a system’s error performance.

Bit-Error Rate

23)

The process of monitoring data transmission and deter mining when errors have occurred. It neither correct errors nor identify which bits are in error-they only indicate when an error has occurred.

Error Detection

24)

Adding of bits for the sole purpose of detecting errors Types of redundancy checks:  vertical redundancy checking,  checksum,  longitudinal redundancy checking  cyclic redundancy checking Prepared By : MARY JANE R. ROGELIO

Single Bit Errors

Multiple-bit error

Burst Error

Probability of Error

Redundancy Checking

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25)

A form of error detection by duplicating each data unit for the purpose of detecting errors.

26)

An error detection bit.

27) 28)

The simplest error-detection scheme and is generally referred to as character parity.

29)

An error detection bit in each character.

30)

The parity bit which is always a 1.

Marking Parity

31)

The parity bit which is not sent or checked

Ignored Parity

32

Form of redundancy error checking where each character has a numerical value assigned to it.

33)

A redundancy error detection scheme that uses parity to determine if a transmission error has occurred with n a message.

34)

An error occurred within a message.

35)

The group pf characters that comprise a message

36)

The bit sequence for the LRC.

37)

A convolution coding scheme that is most reliable redundancy checking technique for error detection. Almost 99.999% of all transmission errors are detected

38)

Types of Error Messages.

Prepared By : MARY JANE R. ROGELIO

Redundancy

Parity Vertical Redundancy Checking (VRC)

Parity Bit

Checksum

Longitudinal Redundancy Checking (LRC) Message Parity Block or Frame of Data Block Check Sequence (BCS) or Frame Check Sequence (FCS)

Cyclic Redundancy Checking

Lost Message Damaged Message

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39)

One that never arrives at the destination or one that is damaged to the extent that it is unrecognizable.

Lost message

40)

One that is recognized at the destination but contains one or more transmission errors.

Damaged Message

It includes enough redundant information with each transmitted message to enable the receiver to determine hen an error has occurred. 41)   

Examples: Parity bits block and frame check characters cyclic redundancy characters

Error-Detecting Codes

It includes sufficient extraneous information along with each message to enable the receiver to determine hen an error has occurred and which bits is in error. 42)

Error-correcting Codes Two primary methods for error correction:  Retransmission  Forward Error Correction

43)

When a receive station requests the transmit station to resend a message when the message is received in error.

A two-way radio term which automatically a retransmission f the entire message. Types of ARQ: 44)

 

Discrete Continuous

Prepared By : MARY JANE R. ROGELIO

Retransmission

Automatic Repeat Request (ARQ) or Automatic Retransmission Request

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The recipient of data sends a short message back to the sender acknowledging receipt of the last transmission. 45) Types of acknowledgements:  Positive  Negative

46)

A receive station becomes the transmits station such as when acknowledgments are sent or when retransmission are sent in response to a negative acknowledgment.

47)

It uses acknowledgments to indicate the successful or unsuccessful reception of data.

48)

It can be used when messages are divided into smaller lock or frames that are sequentially numbered and transmitted in succession, without waiting for acknowledgments between blocks.

49)

The sending station does not receive an acknowledgment after a predetermined length of time.

50)

The destination station asynchronously requests the retransmission of specific frame of data and still be able to reconstruct the entire message once all frames have been successfully transported through the system.

51)

The error-correction scheme that detects and corrects transmission errors when they are received without requiring a retransmission.

52)

A mathematician who was an early pioneer in the development of error-detection and correction procedures, developed the Hamming Code while working at Bell Telephone Laboratories. Prepared By : MARY JANE R. ROGELIO

Acknowledgement

Line Turnarounds

Discrete ARQ

Continuous ARQ

Retransmission Time-Out

Selective Repeat

Forward Error Correction (FEC)

Richard W. Hamming

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53)

An error-correcting code used for correcting transmission errors in synchronous data streams. It requires the addition of overhead to the message, consequently increasing the length of a transmission.

54)

Inserted into a character at random locations.

Hamming Bits

55)

The combination of the data bits and the hamming bits.

Hamming Code

56)

It means to harmonize, coincide, or agree in time.

Synchronize

57)

Involves identifying the beginning and end of a character with in a message.

58)

Its literal meaning is “without synchronism”. In Data Com, it means “without a specific time reference”

59)

Asynchronous communications is called as such because each data character is framed between start and stop bits.

60)

A condition when the transmit and receive clocks are substantially different

Clock Slippage

61)

It occurs when the transmit clock is substantially lower than the receive clock.

Under slipping

62)

Occurs when the transmit clock is substantially higher than the receiver clock.

63)

It involves transporting serial data at relatively high speeds in groups pf characters.

Prepared By : MARY JANE R. ROGELIO

Hamming Code

Character Synchronization

Asynchronous

Start-stop Transmission

Overslipping

Synchronous Data

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POTS

65)

Plain old Telephone system

66)

It is comprised of three basic elements: transmitter (source)  transmission path (data channel)  receiver (destination) 3 fundamental components of endpoints:  data terminal equipment  data communications equipment  serial interface

67)

It can be virtually any binary digital device that generates transmits, receives, or interprets data messages. It is where information originates or terminates.

68)

Devices used to input, output and display information such as keyboards, printers and monitors

69)

Basically a modern-day terminal with enhance computing capabilities

70)

High-powered, high capacity mainframe computers that support terminals.

Hosts

71)

It functions as modern-day host.

Servers

72)

A general term use to describe equipment that interfaces data terminal equipment to a transmission channel, such as a digital T1 carrier or an analog telephone circuit. It is a signal conversion device, as it converts signals from a DTE to a form more suitable to be transported over transmission channel.   

Data Communications System

Data Terminal Equipment (DTE)

Terminal

Client

Equipment (DCE) Data Communications

Types of DCE: channel service units (CSUs) Digital service units (DSUs) data modems

Prepared By : MARY JANE R. ROGELIO

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73)

Another term for DCE.

74)

A DCE used to interface a DTE to an analog telephone circuit commonly called POTS.

Electronic Communications System By Wayne Tomasi

Data Circuit-terminating Equipment (DCTE)

Data Modem

75)

It controls data flow between several terminal devices and the data communications channel.

Cluster Controller

76)

Line control units at secondary stations.

Station Controllers (STACOs)

77)

Universal Asynchronous Receiver/transmitter it is designed for asynchronous data transmission.

78)

A special purpose UART chip manufactured by Motorola.

79)

It means that an asynchronous data format is used and no clocking information transferred between the DTE and the DCE.

80)

An n-bit data register that keeps track of the status of the UART’s transmits and receive buffer registers.

81)

Transmit shift register has completed transmission of data character.

82)

83)

Set when a received character has a parity error in it. Set when a character is received without any or with improper number of stop bits.

Prepared By : MARY JANE R. ROGELIO

UART

Asynchronous Communications Interface Adapter (ACIA) Asynchronous Data Transmission

Status Word

Transmit Buffer Empty (TBMT)

Receive Parity Error (RPE) Receive Framing Error an (RFE)

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84)

Set when a character in the receive buffer register is written over by another receive character.

85)

A data character has been received and loaded into the receive data register.

86)

The difference in time between the beginning of a start bit and when it is detected.

87)

88)

89)

It is used for synchronous transmission of data between a DTE and a DCE. Functions of USRT:  Serial to parallel and parallel to serial data conversions  Error detection by inserting parity bits in the transmitter and checking parity bits in the receiver.  Insert and detect unique data synchronization (SYN) characters  Formatting data in the transmitter and receiver.  Provide transmit and receive status information to the CPU.  Voltage-level conversion between the DTE and the serial interface and vice versa.  Provide a means of achieving bit and character synchronization.

It should provide the ff:  A specific range of voltages for transmit and receive signal levels  Limitations for the electrical parameters of the transmission line.  Standard cable and cable connectors  Functional description of each signal on the interface. In 1962, standardized the interface equipment between data terminal equipment and data communications equipment.

Prepared By : MARY JANE R. ROGELIO

Receiver Overrun (ROR)

Receive Data Available (RDA)

Detection Error

Universal Synchronous Receiver/transmitter (USRT)

Serial Interface

Electronics Industries Association (EIA)

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Electronic Communications System By Wayne Tomasi

It means “Recommended Standards”

92)

The official name of the RS-232 interface

93)

In, 1969, the third revision which was published and remained the industrial standard until 1987.

94)

Sometimes referred to as the EIZ-232 standard Versions D and E of the RS-232 standard changed some of the pin designations.

It is a sheath containing 25 wires with a DB25P-compatible male connector (plug) on one end and a DB25S-compatible female connector (receptacle) on the other end. 95)

RS

Interface Between Data Terminal Equipment and Data Communications Equipment Employing Data Communications Equipment Employing Serial Binary Interchange

RS-232C

RS-232D

RS-232 Cable

Two full-duplex channels:  Primary data-actual information  secondary data-diagnostic information and handshaking signals

96)

It is designed for transporting asynchronous data between a DTE and a DCE or between DTEs .

97)

It is designed for transporting either synchronous or asynchronous data between a DTE and a DCE.

98)

It is designed exclusively for dial-up telephone. It is used for transporting asynchronous data between a DTE and a DCE when the DCE is connected directly to a standard two-wire telephone line attached to the public switched telephone network. Prepared By : MARY JANE R. ROGELIO

9-pin Version of RS-232

25 pin Version

EIA-561

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99)

Electronic Communications System By Wayne Tomasi

It converts the internal voltage levels from the DTE and DCE to RS-232 values.

A voltage leveler wherein its output signals onto the 100) cable.

101) It accepts signals from the cable.

Protective ground, frame ground, or chassis 102) ground.

Voltage-Leveling Circuits

Driver

Terminator

FUNCTIONS OF RS-232 PINS Pin 1

103) Transmit data or send data.

Pin 2

104) Receive data (RD or RxD)

Pin 3

105) Request to send (RS or RTS)

Pin 4

106) Clear to send.(CS or CTS)

Pin 5

107) Data set ready or modem ready.(DSR or MR)

Pin 6

108) Signal ground or reference ground.

Pin 7

109) Unassigned and non-EIA specified often held at +12V

Pin 8

110)

Receive line signal detect, carrier detect or data carrier detect (RLSD, CD or DCD)

111)

Unassigned and often held at -12 Vdc for test purposes

Prepared By : MARY JANE R. ROGELIO

Pin 9

Pin 10

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Secondary receive line signal detect, secondary 112) carrier detect or secondary data carrier detect (SRLSD, SCD, or SDCD) 113) Secondary clear to send. 114)

115)

Secondary transmit data or secondary send data

Transmission signal element timing or serial Clock transmit.

116) Secondary received data 117) Receiver signal element timing or serial clock receive

Pin 12

Pin 13 Pin 14 Pin 15

Pin 16

Pin 17

118) Unassigned is used for local loopback signal

Pin 18

119) Secondary request to send

Pin 19

120) Data terminal ready.

Pin 20

121) Signal quality detector.

Pin 21

122) Ring indicator (RI)

Pin 22

123) Data signal rate selector (DSRS)

Pin 23

Transmit signal element timing or serial clock 124) transmit-DTE

Pin 24

Unassigned. It is sometimes used as a control signal from the DCE to the DTE to indicate that the DCE is in 125) either the remote or local loop back mode.

Prepared By : MARY JANE R. ROGELIO

Pin 25

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It specifies a 37-pin primary connector DB37 and a 9 pin secondary connector DB9 for a total of 46 pins which provides more functions, faster data transmission rates and spans greater distances than the RS-232.    126)     

 

Primary goals of RS-449: Compatibility with the RS-232 interface standard Replace the set of circuit names and mnemonics Provide separate cables and connectors Reduce crosstalks offer higher data transmission longer distances over twisted pair cables loopback capable improve performance and reliability specify a standard connector

RS-449 Serial Interface

Two categories: Category I Category II

Used by the DTE to request a local loopback from the 127) DCE.

10 CIRCUITS IN RS-449 1.Local Loopback

128

Used by the DTE to request a remote loopback from the distant DCE.

Allows the DTE to select the DCE’s transmit and receive frequencies.

129)

Used by DTE to signal the DCE that a test is in progress.

130) Common return wire for unbalanced signals propagating from the DCE to the DTE

Prepared By : MARY JANE R. ROGELIO

2.Remote Loopback

3. Select frequency

4.Test Mode

5. Receive Common

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131)

Used by the DTE to signal the DCE whether it is operational

132)

Used by the DTE to request that the DCE switched to standby equipment.

133)

Used with a modem at the primary location of a multipoint data circuit.

136)

It was intended to operate at data rates between 20 kbps and 2 Mbps using the same DB25 connector

It is used to interface computers, computer networks to analog transmission media Alternate names: 137)  datasets  dataphones  modems

A contraction derived from the words Modulator and Demodulator. Primary Block of a Modem:  Serial interface Circuit  Modulator Circuit 138)  Bandpass filter and equalizer circuit  telco interface circuit  demodulator circuit  carrier and clock generation circuit

139)

Data communications modems designed to operate over the limited bandwidth of the PSTN.

140) It is able of transporting higher bit rates.

141) Digital to analog converter.

Prepared By : MARY JANE R. ROGELIO

6. Terminal in Service

7. Select Standby

8. New Signal

RS-530 Serial Interface

Data Communications Modem

Modem

Voice-band Modem

Broadband Modem

DAC

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142) Analog to digital converter.

It is a rate of change of signals on the transmission 143) medium after encoding and modulation have occurred

144)

Refers to the rate of change of a digital information signal.

ADC

Baud

Bit Rate

145) It is classified as low-speed voice-band modems

Asynchronous Modems

146)

Synchronous data transported by asynchronous modems.

Isochronous Transmission

147)

It uses PSK or quadrature amplitude modulation to transport data.

Synchronous Modems

148)

A special, internally generated bit pattern in transmit modem.

149)

Located in the transmit section of a modem and provide pre-equalization

Training Sequence

Compromise Equalizers

Located in the receiver section of a modem where 150)

151)

Adaptive Equalizer they provide post-equalization to the received signals

The first internationally accepted standard fro 9600bps data transmission rate.

It is intended to provide synchronous data 152) transmission over four-wire leased lines.

Prepared By : MARY JANE R. ROGELIO

ITU-T V.29

V.29 Standard

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153) Five bits.

Quin bits

A technique for full-duplex operation over two wire 154) switched telephone lines.

It address asynchronous-to synchronous transmission conversions and error control that includes both 155) detection and correction. It specifies a new protocol called Link Access Procedures for Modems.

Echo Cancellation

V.32 Specification

It is the next generation data transmission with data rates of 28.8 Kbps without compression possible using V.34. 156)

V.34 Innovations: Nonlinear coding multidimensional coding and constellation shaping  Reduced complexity  precoding of data  line probing  

An enhanced standard adopted by ITU in 1996. It adds 31.2 kbps and 33.6 kbps to the V.34 157) specification.

Developed by ITU-T in February 1998 during a meeting in Geneva, Switzerland. It defines an asymmetrical data transmission technology where 158) the upstream 33.6kbps and downstream of 56kbps.

Prepared By : MARY JANE R. ROGELIO

V.fast

V.34+

V.90 Recommendation

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A new modem standard in 2000 which offers 3 improvements over V.90 that can be achieved only if both the transmit and receive modems and the internet Service Provider(ISP) are compliant. 159)

It offers:  upstream transmission rate of 48 kbps  faster call setup capabilities  incorporation of a hold option

Prepared By : MARY JANE R. ROGELIO

V.92 Recommendation

166